This article is about the information storage unit. For the homophone, see bite. For other uses, see Byte (disambiguation). The byte (pronounced /ˈbaɪt/), is a unit of digital information in computing and telecommunications, that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer12 and it is for this reason the basic addressable element in many computer architectures. The size of the byte has historically been hardware dependent and no definitive standards exist that mandate the size. The de facto standard of eight bits is a convenient power of two permitting the values 0 through 255 for one byte. Many types of applications use variables representable in eight or fewer bits, and processor designers optimize for this common usage. The popularity of major commercial computing architectures have aided in the ubiquitous acceptance of the 8-bit size. The term octet was defined to explicitly denote a sequence of 8 bits because of the ambiguity associated with the term byte. Contents 1 History 2 Unit symbol 3 Unit multiples 4 Common uses 5 See also 6 References // History

The term byte was coined by Dr. Werner Buchholz in July 1956, during the early design phase for the IBM Stretch computer.34 It is a respelling of bite to avoid accidental mutation to bit.1 Early computers were designed for 4-bit BCD code (binary coded decimal) or 6-bit code for printable "graphic set", which included 26 alphabetic characters (only uppercase), 10 Numerical digits, and from 11 to 25 special graphic symbols. To include the control characters and allow digital devices to communicate with each other and to process, store, and communicate character-oriented information such as written language, and lowercase characters, a 7-bit ASCII code was introduced (see ASCII history). Since with just only one bit more an eight bits allows two four-bit patterns to efficiently encode two digits with binary coded decimal, the eight-bit EBCDIC (see EBCDIC history) character encoding was later adopted and promulgated as a standard by the IBM in the System/360, the preset byte. The size of a byte was at first selected to be a multiple of existing teletypewriter codes, particularly the 6-bit codes used by the U.S. Army (Fieldata) and Navy.

In 1963, to end the use of incompatible teleprinter codes by different branches of the U.S. government, ASCII, a 7-bit code, was adopted as a Federal Information Processing Standard, making 6-bit bytes commercially obsolete. In the early 1960s, AT&T introduced digital telephony first on long-distance trunk lines. These used the 8-bit µ-law encoding. This large investment promised to reduce transmission costs for 8-bit data. The use of 8-bit codes for digital telephony also caused 8-bit data "octets" to be adopted as the basic data unit of the early Internet. In the late 1970s, microprocessors such as the Intel 8008 (the direct predecessor of the 8080, and then the 8086 used in early PCs) could perform a small number of operations on four bits, such as the DAA (decimal adjust) instruction, and the half carry flag, which were used to implement decimal arithmetic routines. These four-bit quantities were called nibbles, in homage to the then-common 8-bit bytes. Reasons for the ubiquity of the eight-bit byte include the popularity of the IBM System/360 architecture, introduced in the 1960s, and the 8-bit microprocessors, introduced in the 1970s.

The term octet is used to unambiguously specify a size of eight bits, and is used extensively in protocol definitions, for example. Unit symbol Prefixes for bit and byte multiples Decimal Value SI 1000 k kilo 10002 M mega 10003 G giga 10004 T tera 10005 P peta 10006 E exa 10007 Z zetta 10008 Y yotta Binary Value IEC JEDEC 1024 Ki kibi K kilo 10242 Mi mebi M mega 10243 Gi gibi G giga 10244 Ti tebi 10245 Pi pebi 10246 Ei exbi 10247 Zi zebi 10248 Yi yobi The unit symbol for the byte is specified in IEEE 1541 and the Metric Interchange Format5 as the upper-case character B, while other standards, such as the International Electrotechnical Commission (IEC) standard IEC 60027, appear silent on the subject. In the International System of Units (SI), B is the symbol of the bel, a unit of logarithmic power ratios named after Alexander Graham Bell. The usage of B for byte therefore conflicts with this definition. It is also not consistent with the SI convention that only units named after persons should be capitalized. However, there is little danger of confusion because the bel is a rarely used unit. It is used primarily in its decadic fraction, the decibel (dB), for signal strength and sound pressure level measurements, while a unit for one tenth of a byte, i.e. the decibyte, is never used.

The unit symbol kB is commonly used for kilobyte, but may be confused with the common meaning of kb for kilobit. IEEE 1541 specifies the lower case character b as the symbol for bit; however, the IEC 60027 and Metric-Interchange-Format specify bit (e.g., Mbit for megabit) for the symbol, a sufficient disambiguation from byte. The lowercase letter o for octet is a commonly used symbol in several non-English languages (e.g., French6 and Romanian), and is also used with metric prefixes (for example, ko and Mo) Today the harmonized ISO/IEC 80000-13:2008 – Quantities and units — Part 13: Information science and technology standard cancels and replaces subclauses 3.8 and 3.9 of IEC 60027-2:2005, namely those related to Information theory and Prefixes for binary multiples. Unit multiples Percentage difference between decimal and binary interpretations of the unit prefixes grows with increasing storage size. See also: Binary prefix There has been considerable confusion about the meanings of SI (or metric) prefixes used with the unit byte, especially concerning prefixes such as kilo (k or K) and mega (M) as shown in the chart Prefixes for bit and byte. Since computer memory is designed with binary logic, multiples are expressed in powers of 2, rather than 10. The software and computer industries often use binary estimates of the SI-prefixed quantities, while producers of computer storage devices prefer the SI values. This is the reason for specifying computer hard drive capacities of, say, 100 GB, when it contains 93 GiB of storage space.

While the numerical difference between the decimal and binary interpretations is small for the prefixes kilo and mega, it grows to over 20% for prefix yotta, illustrated in the linear-log graph (at right) of difference versus storage size. Common uses The byte is also defined as a data type in certain programming languages. The C and C++ programming languages, for example, define byte as an "addressable unit of data large enough to hold any member of the basic character set of the execution environment" (clause 3.6 of the C standard). The C standard requires that the char integral data type is capable of holding at least 255 different values, and is represented by at least 8 bits (clause 5.2.4.2.1). Various implementations of C and C++ define a byte as 8, 9, 16, 32, or 36 bits.78 The actual number of bits in a particular implementation is documented as CHAR_BIT as implemented in the limits.h file. Java's primitive byte data type is always defined as consisting of 8 bits and being a signed data type, holding values from −128 to 127. In data transmission systems, a contiguous sequence of binary bits in a serial data stream, such as in modem or satellite communications, which is the smallest meaningful unit of data. These bytes might include start bits, stop bits, or parity bits, and thus could vary from 7 to 12 bits to contain a single 7-bit ASCII code. See also Data hierarchy Primitive data type Nibble References ^ a b Bemer, RW; Buchholz, Werner (1962), "6, Character Set", in Buchholz, Werner (PDF), Planning a Computer System – Project Stretch, http://archive.computerhistory.org/resources/text/IBM/Stretch/pdfs/Buchholz_102636426.pdf . ^ Bemer, RW (1959), "A proposal for a generalized card code of 256 characters", Communications of the ACM 2 (9): 19–23 . ^ Werner Buchholz (July 1956). "Timeline of the IBM Stretch/Harvest era (1956–1961)". Computer History. http://archive.computerhistory.org/resources/text/IBM/Stretch/102636400.txt.  ^ "byte definition". http://catb.org/~esr/jargon/html/B/byte.html.  ^ Metric-Interchange-Format ^ "When is a kilobyte a kibibyte? And an MB an MiB?". The International System of Units and the IEC. International Electrotechnical Commission. http://www.iec.ch/zone/si/si_bytes.htm. Retrieved August 30, 2010. ) ^ [26] Built-in / intrinsic / primitive data types, C++ FAQ Lite ^ Integer Types In C and C++ v · d · eUnits of information Base units Bit · Byte Related units Nibble · Word · Octet Traditional bit units Kilobit · Megabit · Gigabit · Terabit · Petabit · Exabit · Zettabit · Yottabit Traditional byte units Kilobyte · Megabyte · Gigabyte · Terabyte · Petabyte · Exabyte · Zettabyte · Yottabyte IEC bit units Kibibit · Mebibit · Gibibit · Tebibit · Pebibit · Exbibit · Zebibit · Yobibit IEC byte units Kibibyte · Mebibyte · Gibibyte · Tebibyte · Pebibyte · Exbibyte · Zebibyte · Yobibyte v · d · eData types Uninterpreted Bit · Byte · Trit · Tryte · Word Numeric Integer · Fixed-point · Floating-point · Rational · Complex · Bignum · Interval Text Character · String Pointer Address · Reference Composite Algebraic data type (generalized) · Array · Associative array · Class · List · Object · Option type · Product · Record · Set · Union (tagged) Other Boolean · Bottom type · Collection · Enumerated type · Exception · First-class function · Opaque data type · Recursive data type · Semaphore · Stream · Top type · Type class · Unit type · Void Related topics

Abstract data type · Data structure · Interface · Kind (type theory) · Primitive data type · Subtyping · Template · Type constructor · Parametric polymorphism

Abstract data type · Data structure · Interface · Kind (type theory) · Primitive data type · Subtyping · Template · Type constructor · Parametric polymorphism

Abstract data type · Data structure · Interface · Kind (type theory) · Primitive data type · Subtyping · Template · Type constructor · Parametric polymorphism

Abstract data type · Data structure · Interface · Kind (type theory) · Primitive data type · Subtyping · Template · Type constructor · Parametric polymorphism